Method and apparatus for monitoring well pumping units

ABSTRACT

Method and apparatus for monitoring the operation of a sucker rod-type pump employed in withdrawing fluids from a well. A transducer is employed to generate a signal representative of the load in the pumping unit as the rod string is reciprocated to operate a downhole pump. This signal is differentiated in order to produce a derivative function which is representative of the rate of change of the load signal. The derivative function is analyzed to detect indications of fluid pounding of the well. When a given condition of fluid pounding is encountered, a monitor function is produced which is employed to initiate action such as temporarily shutting down the pumping unit or activating an alarm. The signal from the transducer also is analyzed for a normal high load amplitude and for amplitudes which fall outside of a desired maximum-minimum load range. The invention may be implemented by hardwired or software systems.

O Unlted States Patent 1111 3,838,597 Montgomery et al. 1 Oct. 1, 1974[54] METHOD AND APPARATUS FOR [57] ABSTRACT MONITORING WELL PUMPINGUNITS Method and apparatus for monitoring the operation of [75]Inventors: Richard C. Montgomery; Jacque R. a Sucker r ype pump employedin withdrawing flu- Stoltz, both of Midland, Tex. ids from a well. Atransducer is employed to generate a signal representative of the loadin the pumping unit [73] Asslgnee' gi Corporatlon New York as the rodstring is reciprocated to operate a downhole l pump. This signal isdifferentiated in order to produce [22] Filed: Dec. 28, 1971 aderivative function which is representative of the rate of change of theload signal. The derivative func- [21] Appl 213397 tion is analyzed todetect indications of fluid pounding of the well. When a given conditionof fluid pounding [52] US. Cl. 73/151 is encountered, a monitor functionis produced which [51] Int. Cl E2lb 47/00 is employed to initiate actionsuch as temporarily shut- [58] Field of Search 73/151, 141 R, 141 A tingown the pumping unit or activating an alarm. The signal from thetransducer also is analyzed for a [56] References Cited normal high loadamplitude and for amplitudes which UNITED STATES PATENTS fall outside ofa desired maximum-minimum load 2107 151 2/1938 Higginson 73/15] X range.The invention may be implemented by hard- 2,163,665 6/1939 Carr et al73/151 or Software Systems- 2,661,697 12 1953 Long et al 73/151 uxPrimary Examiner-Jerry W. Myracle Attorney, Agent, or Firm-Andrew L.Gaboriault;

William D. Jackson 27 Claims, 5 Drawing Figures mmmw W 3.838.597

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Y AIEmwnm H914 umw METHOD AND APPARATUS FOR MONITORING WELL PUMPINGUNITS BACKGROUND OF THE INVENTION This invention relates to themonitoring of sucker rod-type well pumping units and more particularlyto processes and systems for monitoring the operation of such units byoperating on a transducer signal representative of load changes in theunits.

Sucker rod-type pumping units are widely used in the petroleum industryin order to recover fluids from wells extending into subterraneanformations. Such units include a sucker rod string which extends intothe well and means at the surface of the well for reciprocating the rodstring in order to operate a downhole pump, Typical of such units arethe so-called beam-type pumping units. In a beam-type pumping unit thesucker rod string is suspended at the surface of the well from astructure consisting of a sampson post and a walking beam pivotallymounted on the sampson post. The sucker rod string normally is connectedat one end of the walking beam which is connected also to a prime moverthrough a suitable crank and pitman connection. Thus by this arrangementthe walking beam and the sucker rod string are driven in a reciprocalmode by the prime mover.

In order to analyze and/or control the performance of a well produced bymeans of a rod-type pumping unit, it is a conventional practice tomeasure, either directly or indirectly, the load on the rod string asthe unit is in operation. One particularly useful system by which thismay be accomplished is disclosed in U.S. Pat'. application Ser. No.58,439, entitled WELL MON ITORING APPARATUS, filed July 27, 1970, byRichard C. Montgomery and J acque R. Stoltz, the inventors herein. Inthe system disclosed in said application Ser. No. 58,439 a transducer issecured to the walking beam of a beam pumping unit in order to generatea signal representative of the load in the beam as it is reciprocated.The load changes in the beam in a representative and repeatablerelationship with the load in the sucker rod string such that theinformation derived from the transducer may be employed to characterizethe well as to normal or abnormal operating conditions. The transducersignal may be recorded for future analysis or it may be used for realtime control of the pumping unit.

Another more conventional technique for obtaining an indication of loadmeasurements in the sucker rod string is to employ a transducer,commonly termed a pump dynamometer, which is attached directly in thesucker rod string, normally in the polished rod" section thereof. Forexample, U.S. Pat. No. 3,359,791 to Pantages discloses a pumpdynamometer which is mounted in the polished rod section of the rodstring and which functions to generate an alarm or to initiate a controlaction in response to the dynamometer output reaching a condition of anabnormally high or low load on the polished rod or failing to reach acondition representative of an intermediate normal load condition withina specified time interval. Thus when the control system in Pantagesindicates an abnormally high or abnormally low load condition, a signalis generated to shut down the pump. Signals indicative of normaloperating loads are applied through time delay devices such that if suchsignals are not received within a given time interval appropriate actionmay be taken such as shutting down the pump or activating an alarm. Ithas also been proposed to take such control measures through the actionof a central control facility. For example, as described by Boggus, C.C., Lets Weigh Those Wells Automatically, OIL & GAS JOURNAL, Vol. 62,No. 5, Feb. 3, 1964, p. 78, the output from a large number of pumpdynamometers can be applied to a central computer which is programmed totake appropriate control actions.

One abnormal pumping condition to which much attention has been given isthe phenomenon termed fluid pounding. Fluid pounding occurs when thewell pumps off, i.e., when fluid is withdrawn from the well at a rategreater than the rate at which it enters the well from the formation.When this occurs, the working barrel of the downhole pump is onlypartially filled during an upstroke of the plunger. Then on thedownstroke the plunger strikes or pounds the fluid in the workingbarrel. This causes severe jarring of the entire pumping unit, includingthe rod string and the surface equipment, which ultimately may lead tofailure of the unit.

Various techniques have been proposed for monitoring a rod-type pumpingunit in order to avoid or sense the fluid pound condition. Exemplary ofsuch systems is the one disclosed in U.S. Pat. No. 3,509,824 to Schmidlywhich may be employed for pumping units in which an electric motor isemployed as the prime mover. This system employs a transducer whichgenerates an output signal indicative of the power demand of the motor.The output from the transducer is applied to an overload sensor" whichtakes appropriate con trol action in the case of an unacceptable powerdemand by the electric motor. The output from the transducer also isapplied to an underload sensor which is indicative of low powerconsumption of the motor such as may be due to fluid pounding. A pulsesignal output from the underload sensor is applied through a gatingarrangement to a pulse integrator which does not time out so long as theunderload sensor fails to detect low power consumption indicative of anunacceptable condition of fluid pounding.

Another type of system for detecting fluid pounding is disclosed in U.S.Pat. No. 3,559,731 to Stafford. The Stafford system employs a flowindicator in the flow line leading from the wellhead to the surfacegathering system. The output from the flow indicator is applied througha suitable time delay relay such that if fluid flow does not occurthrough the flow line within a desired time interval, the delay trips toshut in the well. Various other systems have been employed to detectfluid pounding of a pumping unit or conditions commonly associated withfluid pounding. For a further description of such systems, reference ismade to U.S. Pat. Nos. 3,075,466 to Agnew et al., 3,269,320 to Tilley etal., and 3,306,210 to Boyd et al.

SUMMARY OF THE INVENTION This invention provides new and improvedmethods and apparatus for monitoring the operation of a well pumpingunit of the type employing a sucker rod string and means to reciprocatethe rod string to operate a downhole pump. In carrying out theinvention, there is employed a transducer to generate a signalrepresentative of a changing load in the pumping unit as the rod stringis reciprocated. The signal from the transducer is operated on toproduce an operating function which is representative of the rate ofchange of the load signal. A monitor function, otherwise referred toherein as a control function, is then generated in response to theoperating function reaching a condition indicative of a specifiedcondition of fluid pounding which is deemed undesirable. This monitor orcontrol function may be employed to initiate appropriate control and/oralarm action.

In a further aspect of the invention, the load signal also is operatedupon to amplitude discriminate the load signal with respect to a givenhigh amplitude discrimination value indicative of a minimum acceptablehigh load condition. A monitor or control function is generated upon thefailure of the load signal failing to reach this value within a desiredfrequency condition.

In yet a further embodiment of the invention, the load signal also iscompared with an amplitude range having upper and lower amplitude limitswhich are above and below, respectively, the aforementioned amplitudediscrimination value. A monitor or control function is generated inresponse to the amplitude of the load signal falling outside of thisrange which corresponds to acceptable high and low load conditions.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is an illustration of a wellequipped with a sucker rod-type pumping unit.

FIG. 2 is an illustration showing in block diagram the functionalcomponents of a preferred embodiment of the invention.

FIG. 3 is an illustration of waveforms as they may appear in certainlocations of the diagram of FIG. 2.

FIG. 4 is an illustration of waveforms which appear in a furtherembodiment of the invention.

FIG. 5 is an electrical schematic of an embodiment of the inventionemploying hardwired logic circuitry.

DESCRIPTION OF SPECIFIC EMBODIMENTS Perhaps the most commonly employedrod pumping units are beam units of the so-called conventional type" andthe invention will be described in detail with respect to its use inconjunction with this type of unit. Referring first to FIG. 1, there isillustrated the wellhead of a well which extends from the earths surface12 into a subterranean oil producing formation (not shown). The wellheadcomprises the upper portions of a casing string 14 and tubing string 16.The tubing string extends from the wellhead to a suitable depth withinthe well, e.g., adjacent the subterranean formation. Liquid from thewell is produced through the tubing string 16 by means of a downholepump (not shown) to the surface where it passes into a flowline 17.

The downhole pump is actuated by reciprocal movement of a sucker rodstring 18. Rod string 18 is suspended in the well from a surface supportunit 20 comprising a sampson post 21 and a walking beam 22 which ispivotally mounted on the sampson post by a pin connection 23. The suckerrod string includes a polished rod section 180 which extends through astuffing box (not shown) at the top of the tubing string and a section1812 formed of flexible cable. The cable section 18b is connected to thewalking beam 22 by means of a horsehead" 24.

The pumping unit is driven by a prime mover 26 such as an electricmotor. The prime mover drives the walking beam through a drive systemwhich includes a belt drive 27, crank 28, crank arm 29, and a pitman 30which is pivotally connected between the crank arm and walking beam bymeans of pin connections 32 and 33. The outer end of crank arm 29 isprovided with a counterweight 35 which balances a portion of the load onthe sucker rod string in order to provide for a fairly consistent loadon the prime mover.

It will be recognized that the well structure and pumping equipment thusfar described are conventional and merely exemplary, and that thepresent invention may be employed with respect to other suitablerod-type pumping units. For a more detailed description of suchequipment. reference is made to Uren, L. C., PETROLEUM PRODUCTIONENGINEERING OIL FIELD EXPLOITATION, Third Edition. McGraw-Hill BookCompany, Inc., New York, Toronto, and London, I953, and moreparticularly to the description of rod-type pumping units appearing inChapters VI and VII thereof.

Turning now to FIG. 2, there is illustrated in block diagram a preferredembodiment of the present invention. This embodiment comprises atransducer 40 which may be connected to the pumping unit at anyappropriate location as described hereinafter, an operating unit 42 towhich the transducer signal is applied, and a control unit 44 whichresponds appropriately to control functions from the operating unit. Theoperating unit comprises a first section 42a which functions to generatea control function indicative of a fluid pound condition, a secondsection 42b which generates a control function when the signal from thetransducer fails to reach a desired high normal load condition, and athird section 420 which generates a control function when the loadsignal exceeds a maximum limit or falls below a minimum limit.

The transducer may be of any suitable type and may be positioned on thepumping unit on any component in which the stress or load changes in arepresentative repeatable manner with load changes in the rod string.

An obvious location for the transducer is, of course, in

the rod string itself. However, it normally will be desirable to employa transducer of the type described in the aforementioned applicationSer. No. 58,439 and to locate the transducer on a load-bearing supportstructure as taught in that application. A preferred location for thetransducer is on the walking beam in the area generally located byreference character 38, between the pivotal connection of the beam onthe sampson post and the horsehead connection.

The operation of the invention will be described in detail withreference to FIG. 2 and with reference to the waveforms shown in FIG. 3.The several waveforms illustrated and the respective points at whichthey appear in FIG. 2 are designated by common reference characters inFIGS. 2 and 3. Referring first to FIG. 2, the transducer 40 generates anoutput signal representative of load changes in the pumping unit as therod string is reciprocated. The output signal from the transducer mayvary, for example, in proportion to the strain induced in the componentupon which it is mounted, within the range of O to 25 millivolts d.c.The transducer signal is applied through a high gain d.c. amplifier 45in order to provide a more easily usable load signal, e.g., one withinthe range of 0 to 5 volts do. This signal is applied to sections 42a,42b, and 420 of the opcrating unit.

In section 42a the load signal from the transducer is first operatedupon in order to arrive at a function representative of the rate ofchange of the signal. This is accomplished in the preferred embodimentof the invention by applying the signal to a differentiator 46 whichproduces a time derivative of the load signal. The amplitude of thederivative function increases as the slope, or rate of change, of theload signal increases.

The output from differentiator 46 is applied to an amplitudediscriminator 47 which functions to amplitude discriminate thederivative signal to produce a residual output function representativeof a predetermined fluid pound condition. Specifically, discriminator 47may take the form of a comparator which compares the differentiatoroutput with a preset reference voltage which corresponds to a desireddiscrimination value. Thus each time the rate of change of thetransducer signal is such as to result in a differentiator output abovethe specified discrimination value, a residual signal pulse is producedby the amplitude discriminator.

The output from the amplitude discriminator 47 is accumulated until itreaches a constraint indicative of an unacceptable fluid poundcondition, at which time a control signal is generated. Morespecifically, the residual function from discriminator 47 is applied toan integrator 48 equipped with a follower trip unit 50. When theaccumulated residual pulses from discriminator 47 reach a specifiedconstraint, such as may be determined by the time constant of theintegrator and the activation level of the trip unit 50, a controlsignal is applied to a pump of relay 52 in control unit 44. Relay 52then initiates appropriate actions as described hereinafter.

Preferably, the residual function from amplitude discriminator 47comprises a plurality of pulses which are characteristicallyproportional to the amplitude differentials between corresponding peaksof the derivative function and the voltage level at which the amplitudediscriminator 47 is set. Thus the pulses from discriminator 47 areproportional in a characteristic such as amplitude or duration, or theproduct of amplitude and duration, to amounts by which the peaks of thesignal from the differentiator exceed the discrimination value. Thismode of operation is advantageous since the constraint at which theintegrator trip operates will then relate quantitatively to the rate ofoccurrence of fluid pounding and also to the magnitude of such fluidpounding. Thus, for a given setting of the integrator trip 50, thecontrol function will be generated upon the occurrence of a given numberof moderate pounding conditions, or upon the occurrence of a lessernumber of more severe pounding conditions.

Turning to FIG. 3, the operation of the differentiator, amplitudediscriminator, and integrator can best be understood by referring tocurves a, b, c, and d which are analog values with amplitude in ordinateand time in abscissa. In FIG. 3, curves b, c, and d are shown in reversepolarity with respect to curve a to provide for easy reference. At timethe load signal a begins to decrease unusually rapidly to a low loadcondition thus indicating the occurrence of fluid pounding. This rapidchange in load is reflected in the differentiator output b which exceedsthe reference voltage setting of amplitude discriminator 47 (indicatedby broken line 54). The residual pulse output from the amplitudediscriminator is indicated by curve c. As is evident from an examinationof curves b and c, the pulses in curve c are of common amplitude, butvary in duration in proportion to the amplitude differentials betweenthe corresponding peaks of signal b and discrimination level 54. Forexample, the relief of peak b, of the differentiator output signal inexcess of level 54 is about one-third of the relief of peak b Thus, theduration of pulse c,, corresponding to peak b is about one-third of theduration of pulse 0 corresponding to peak b It is preferred to employpulse duration as the proportional characteristic since by keeping thepulse amplitude relatively constant, the integrator response is morerepeatable in following the time integral of the applied pulses.

The output from integrator 48 is illustrated by curve d of FIG. 3. Asshown, the integrator output remains flat so long as the differentiatoroutput is flat. When the differentiator output exceeds thediscrimination level 54, the charge on integrator 48 builds up inproportion to the time integrals of pulses c 0 etc. When the integratortrip level (indicated by broken line 55) is reached, a control signal isapplied to relay 52. If fluid pounding ceases before the trip level isreached, the integrator will begin to discharge and the output willreturn to its former level.

From an examination of curve a of FIG. 3, it will be noted that thetransducer signal also undergoes a relatively rapid change during theupstroke of the sucker rod string. this is indicated by segments a a, ofcurve a which reflect decreases in load which may be encountered innormal operation. Depending upon the speed at which the rod string isreciprocated this load change rate during the upstroke of the load mayapproach and sometimes even exceed the load change rate which isindicative of a fluid pound condition. In a preferred embodiment of theinvention, possible erroneous indications from this phenomenon areavoided by equipping the differentiator with an initial clipping unitwhich prevents the peak amplitude of the applied load signal fromexceeding a predetermined value. The clipping unit is set to a referencelimit significantly below the maximum amplitude of the load signal.Preferably, the clipping unit is set to a reference value which is lessthan the discrimination value employed for the normal maximum loaddetermination described in detail below. The clipping unit referencewill, of course, be greater than the low load limit employed in section42c,

The waveforms associated with this embodiment of the invention are inFIG. 4 with curve a illustrating the clipped load signal and curve b theattendant differentiator output. As shown by curve a, the load signal isclipped at a reference level 57, thus eliminating the signal in excessof this amplitude. The clipped signal is then applied to thedifferentiator in order to produce the differentiator output b. As canbe seen by an examination of these signals, 'the rapid change in thetransducer signal during the upstroke of the rod string will not bereflected in the differentiator output.

To summarize briefly the operation of section 42a, the load signal isdifferentiated and the resulting derivative is amplitude discriminatedto detect peak values indicative of fluid pounding. This residual isthen integrated and when the integral reaches a predetermined value, thecontrol function is generated. From the foregoing description it will berecognized that the integration step may be omitted and fluid poundingcan still be detected by responding directly to the amplitudediscrimination of the derivative. However, the integration step ishighly advantageous since it permits a quantita tive determination withrespect to both the frequency and severity of the fluid pounding.

Turning now to the operation of the invention with regard to the normalmaximum load determination, the load signal from amplifier 3 is appliedto an amplitude discriminator 56. Amplitude discriminator 56 is set witha relatively high amplitude discrimination value which is slightly belowthe maximum amplitude of the load signal encountered during normaloperation of the pumping unit. Thus, during normal operation of thepumping unit, the discriminator 56 will produce a residual functioncomprised of one pulse for each cycle of operation of the pumping unit.

The output from discriminator 56 is applied to a timing circuit which isreset by each pulse and which times out to generate a control functionif it is not reset within a desired time interval. More specifically,the timing circuit comprises a passive integrator 58 equipped with afollower trip unit 60. Integrator 58 continuously charges in onedirection and if it is not reset by the residual signal from theamplitude discriminator within a given interval, the integrator outputwill reach the level required to actuate trip 60. Thus it can be seenthat if the load in the pumping unit does not reach some minimum value(corresponding to the discrimination level for discriminator 56) withina desired frequency, trip 60 will operate to generate a controlfunction. This control function is applied to a unit malfunction relay62 in control unit 44.

In addition to the fluid pound and maximum normal load analyses, thepresent invention also provides means for analyzing the load signal foramplitudes indicative of unacceptably high or low loads in the pumpingunit. This is accomplished by applying the load signal to a comparatorwhich functions to compare the load signal with an amplitude rangehaving upper and lower amplitude limits. Upon the amplitude of the loadsignal falling outside of this range, the comparator unit generates acontrol function which is applied to the unit malfunction relay 62 incontrol unit 44.

The comparator circuit unit 64 comprises parallelconnected amplitudediscriminators 65 and 66. Amplitude discriminator 65 is set to adiscrimination level above the discrimination level for discriminator 56and above a signal level associated with acceptable maximum loads.Discriminator 66 is set to a low discrimination level below thediscrimination level of detector 56 and below a signal level associatedwith acceptable minimum loads, Thus in operation of the comparator unit,the load signal is compared with a high preset reference voltage andshould the load signal exceed this voltage, a control signal isgenerated for application to relay 62. The load signal also is comparedin discriminator 66 with a low reference voltage and upon the sig naldropping below this reference voltage, a control function is similarlygenerated and applied to relay 62.

In the control unit 44, the primary control responses are taken by thepump-off relay 52 and the unit malfunction relay 62. When a controlsignal indicative of fluid pounding is applied to relay 52, this relayfunctions to activate a unit shut down relay 68. This relay then acts,e.g., by opening contacts in a power supply circuit if the prime moveris an electric motor, to shut down the prime mover. The relay 52 alsocloses contacts in an alarm circuit 70 in order to energize an alarm,which typically may take the form of a visual indicator. In addition,relay 52 acts to shut down a totalizer 72 which records the running timeof the pumping uniit. Thus. if the unit intermittently pounds and isshut donw, totalizer 72 will indicate only the time during which theunit is actually pujping. Relay 52 also activates a shut down timer 74.Timer 74, which may be a conventional electromechanical timer, is set torun for a preset time interval which will allow sufficient fluid toaccumulate in the well to avoid pounding. When timer 74 times out, ittrips a relay 76 which then functions to reset relay 52 to its formerstate. The actions applied to relay 68, alarm 70, and the run timetotalizer 72 are then released, and these units return to their formerstates. The pumping unit then resumes operation until such time aspounding may again occur.

The unit malfunction relay 62 responds to an applied control function toturn on an alarm 80 and to actuate unit shut down relay 68. The unit inthis situation remains down until relay 62 is manually reset by tripmeans 82.

The control function initiated by integrator trip 50 is also employed todisable the operation of the normal maximum load section 42b. Thisavoids, during the time that the pumping unit is shut down to alleviatethe fluid pounding condition, the generation of a control function bysection 42b. This may be accomplished by action of the pump-off relay52, as shown schematically in FIG. 2. Thus when a control signalindicative of the fluid pounding is applied to relay 52, this relay actsto open a switch 84 in the output from the integrator trip 60. Whenrelay 76 acts to return the pump-off relay to its former state, switch84 will be closed.

The present invention can be carried out employing a hardwired system asdiscussed in greater detail hereinafter, located at the well site. Thisnormally will be desirable where individually isolated wells are to bemonitored. The invention can also be carried out by employing a properlyprogrammed digital computer to implement the analysis and controlfunctions described above with respect to operating unit 42. This modeof operation is advantageous where a large number of wells in an areacan be placed under the control of a central facility.

A digital computing system which is suitable for use in carrying out theinvention is the Data General Corporation Nova" minicomputer equippedwith a 16-bit bidirectional IO bus which provides for input into thecomputer and interfacing between the computer and a master supervisorycontrol system.- Suitable master and remote terminal units which may beemployed are available from Baker Automation Systems, Inc. as the RDACS"Master/Remote system.

In operation, the computer initiates instructions and receivesinformation through the master and remote terminal units to effectmonitoring and control actions with respect to a given well. Forexample, the load signal from the tranducer on the pumping unit may beinterrogated at 0.2-second intervals for a period of l0 seconds. At eachinterrogation, the analog output from the transducer is converted to adigital value by the remote terminal unit and transmitted to the masterunit and computer for analysis by the computer. The computer is, ofcourse, programmed to perform numerically the various analyticaloperations described previously in analog format and to transmitinstructions initiating the appropriate control functions forapplication to the control unit 44, located at the well site.

FIG. illustrates specific circuits which may be employed in a hardwiredoperating unit 42. The circuits in FIG. 5 which correspond to thecomponents shown functionally in FIG. 2 are identified by the prime ofthe reference characters used in FIG. 2. With reference to FIG. 5, theload signal from amplifier 45 (shown in FIG. 2) is applied acrossterminals T1 and T2 to differentiator 46' which is equipped with aninitial clipping circuit comprising a resistor R26, diode D2, and avariable reference potentiometer P8. Potentiometer P8 is set to thedesired reference voltage and signal amplitudes greater than thisreference are not allowed to pass to the capacitor C6. Thedifferentiator 46' comprises an amplifier 4A and a feedback resistor R41in addition tocapacitor C6. The first time derivative of signalspresented at capacitor C6 is available at the output, pin 1, ofamplifier 4A.

The differentiator trip 47' is comprised of an input resistor R40,amplifier 48, variable reference potentiometer P7, and positive feedbackresistor R39. The output of amplifier 4B attains its maximum positivevalue whenever the input to R40 exceeds the reference voltage set bypotentiometer P7. The output of amplifier 48 returns its minimum(maximum negative) value when the input to resistor R40 declines to avalue less than the reference voltage.

The signal from amplifier 4B is applied to integrator 48' which includesamplifier 5B, variable reference potentiometer P9, feedback capacitorC7, resistors R42 and R43, and diode D6. Diode D6 and low level resistorR42 control the integration rate when maximum or pulse input voltage ispresent. High level resistor R43 determines the integration rate when aminimum input occurs. The trip circuit 50' for integrator 48 comprisesan input resistor R27, variable reference potentiometer P5, amplifier5A, and positive feedback resistor R44. The output of amplifier 5Aassumes its maximum positive value when the input to resistor R27exceeds the reference voltage or trip level" set by potentiometer P5 andremains at its minimum value when the input to resistor R27 is less thanthis reference voltage. This output is applied to unit shut down relay52.

The load signal also is applied to amplitude discriminator 56 for thenormal maximum load determination. This unit includes an amplifier 1A,variable reference potentiometer P2, positive feedback resistor R14,input resistor R16, and override resistor R15. When the well is pumping,the output of amplifier 1A goes to its maximum negative value when thesignal input to resistor R16 exceeds the reference voltage determined bypotentiometer P2 and returns to its previous value when the signal inputfalls below this voltage. The integrator 58 is comprised of capacitorC8, resistors R12 and R13, and diode D1. Low level resistor R12 and thediode D1 determine the discharge rate of capacitor C8 and high levelresistor R13 determines the charging rate. The integrator trip circuit60 comprises an amplifier 1B, variable reference potentiometer P1, inputresistor R11, and positive feedback resistor R10. Amplifier 1B attainsits maximum output when the voltage on capacitor C8 exceeds the voltageset by potentiometer P1 and this output is fed to relay 62.

When the pumping unit is shut down by the pump-off relay (shown in FIG.2), a voltage signal is applied at terminal T3 to resistor R15 in orderto disable section 42b from its normal operation. This voltage signal issufficiently greater than the reference voltage determined bypotentiometer P2 so that the absence of a normal maximum load signalduring this time does not result in activation of the integrator trip60. When the well returns to normal operation, the voltage to resistorR15 is removed. Thus it can be seen that this operation is equivalent tothe opening and closing of switch 84 as described above with referenceto FIG. 2.

The high load amplitude discriminator 65' is comprised of amplifier 28,a variable reference potentiometer P4 set to a high load voltage, inputresistor R3, and positive feedback resistor R18. The output of amplifier2B attains its maximum value if the input to resistor R3 exceeds the setpoint. So long as the load signal input to resistor R3 does not exceedthe reference voltage, the output of amplifier 28 remains at its minimumvalue. The output of high load detector 65 is supplied to relay 62.

The transducer signal also is applied to low load amplitudediscriminator 66'. Discriminator 66 functions similarly as discriminator65, but is equipped with an initial inverter 66a comprising inputresistor R22, amplifier 3A, and feedback resistor R23. Inverter 66a actsto reverse the polarity of the load signal before it is applied to inputresistor R17. Thus the output of amplifier 2A goes to its maximum valuewhen the input to resistor R17 exceeds the reference voltage determinedby potentiometer P3 and corresponding to the minimum acceptable load.The output from the amplifier 2A is supplied to relay 62.

In the system shown in FIG. 5, the following circuit parameters may beused. Resistors R3, R15, R16, R27, and R40 22 kilohms; R5, R11, R14,R18, R39, and R44 330 kilohms; R10 2.1 megohms; R12, R22, and R23 l0kilohms; R13 and R45 2.2 megohms; R17, R41, and R43 6.8 megohms; R19 andR 5.1 kilohms; and R26 and R42 47 kilohms. Capacitors C6 and C7 arerated at volts with capacitances, respectively, of 2 microfarads andmicrofarads. Capacitor C8 is a 50-volt 250 microfarad capacitor. Each ofdiodes D1, D2, and D6 is type number IN4009. Potentiometers Pl-P9 arerated at 20 kilohms and each of the amplifiers described is an N5558Tintegrated circurt.

What is claimed is:

1. In a method of monitoring the operation of a well produced by theoperation of a pumping unit including a' sucker rod string and means toreciprocate said rod string to produce fluid from a subterraneanlocation, the steps comprising:

a. generating a signal representative of a changing load in said unit assaid rod string is reciprocated,

b. operating on said signal to produce an operating functionrepresentative of the rate of change of said signal, and

c. generating a monitor function in response to said operating functionreaching a specified condition.

2. The method of claim 1 further comprising the step of, prior to step(b), clipping said load signal with respect to a peak amplitudereference value, and carrying out the operation of step (b) on saidclipped load signal.

3. The method of claim 1 further comprising the step of amplitudediscriminating said operating function to produce a residual functionthereof, accumulating said residual function, and generating saidmonitor function in response to said accumulated residual functionreaching a specified constraint.

4. The method of claim 1 wherein said load signal is differentiated toproduce a derivative of said load signal as said operating function,amplitude discriminating said operating function with respect to adiscrimination value to produce a residual of said operating functioncomprising a plurality of pulses characteristically proportional to theamplitude differentials between the corresponding peaks of saidoperating function and said discrimination value. integrating saidresidual function, and generating said monitor function in response tosaid integrated residual function reaching a specified constraint.

5. The method of claim 4 wherein said pulses are proportional induration to said amplitude differentials.

6. The method of claim 1 further comprising:

comparing said load signal with an amplitude range having an upperamplitude limit and a lower amplitude limit, and

generating a monitor function in response to the amplitude of said loadsignal falling outside of said range. 7. The method of claim 1 furthercomprising: amplitude discriminating said load signal with respect to ahigh amplitude discrimination value, and

generating a monitor function in response to said load signal failing toreach said value within a specifled frequency condition.

8. The method of claim 7 further comprising the step of, prior to step(b) of claim 1, clipping said load signal with respect to a peakamplitude reference value which is less than said high amplitudediscrimination value, and carrying out the operation of step (b) on saidclipped load signal.

9. The method of claim 7 further comprising:

comparing said load signal with an amplitude range having an upperamplitude limit and a lower amplitude limit, said upper amplitude limitbeing greater than said high amplitude discrimination value, and

generating a monitor function in response to the amplitude of said loadsignal falling outside of said range. 10. ln a system for use inmonitoring the operation of a well pumping unit of the type having a rodstring and means for reciprocating said rod string to operate a downholepump, the combination comprising:

transducer means adapted to be connected to a well pumping unit of thetype described for generating a signal representative of a changing loadin said unit, operator means responsive to said load signal forproducing an operating function representative of the rate of change ofsaid load signal, and means responsive to said operating function forgenerating a monitor function upon said operating function reaching aspecified condition. 11. The system of claim 10 further comprising:discriminator means responsive to said load signal for amplitudediscriminating said load signal with respect to a high amplitudediscrimination value to produce a residual of said load signal, and

timing means responsive to the residual output signal from saiddiscriminator means for generating a second monitor function upon saidload signal failing to reach said high amplitude discrimination value 5within a specified frequency condition.

12. The system of claim 11 further comprising: means responsive to saidfirst-named monitor function for disabling the operation of said timingmeans to generate said second-named monitor 0 function.

13. The system of claim 11 further comprising: comparator meansresponsive to said load signal for generating a readout function uponthe amplitude of said load signal falling outside of the upper and lowerlimits of an amplitude range encompassing said high amplitudediscrimination value. 14. In a system for use in monitoring theoperation of a well pumping unit of the type having a rod string andmeans for reciprocating said rod string to operate a downhole pump, thecombination comprising:

transducer means adapted to be connected to a well pumping unit of thetype described for generating a signal representative of load changes insaid unit,

operator means responsive to said load signal for differentiating saidload signal to produce an operat' ing function which is a derivative ofsaid load signal,

means for amplitude discriminating said operating function with respectto a specified discrimination value to produce a residual functioncomprised of a plurality of pulses characteristically proportional tothe amplitude differentials between the corresponding peaks of saidoperating function and said discrimination value,

means responsive to the output from said amplitude discriminating meansfor integrating said residual function, and

means responsive to the output from said integrating means forgenerating a monitor function upon said output reaching a specifiedconstraint.

15. The system of claim 14 wherein said pulses are proportional induration to said amplitude differentials. 45

timing means responsive to the residual output signal from said secondamplitude discriminating means for generating a second monitor functionupon said load signal failing to reach said high amplitudediscrimination value within a specified frequency conditionv 18. Thesystem of claim 17 further comprising comparator means responsive tosaid load signal for generating a third monitor function upon theamplitude of said load signal falling outside of the upper and lowerlimits of an amplitude range encompassing said high amplitudediscrimination value.

19. In a system for monitoring the operation of a well pumping unit ofthe type having a rod string and means for reciprocating said rod stringto operate a downhole pump, the improvement comprising:

transducer means connected to said well pumping unit for generating asignal representative of a changing load in said unit as said rod stringis reciprocated,

operator means responsive to said load signal for producing an operatingfunction representative of the rate of change of said load signal, and

means responsive to said operating function for generating a monitorfunction upon said operating function reaching a specified condition.

20. The system of claim 19 further comprising: discriminator meansresponsive to said load signal for amplitude discriminating said loadsignal with respect to a high amplitude discrimination value to producea re sidual of said load signal, and

timing means responsive to the residual output signal from saiddiscriminator means for generating a second monitor function upon saidload signal failing to reach said high amplitude discrimination valuewithin a specified frequency condition.

21. The system of claim 20 further comprising:

means responsive to said first-named monitor function for disabling theoperation of said timing means to generate said second-named monitorfunction.

22. The system of claim 20 further comprising:

comparator means responsive to said load signal for generating a readoutfunction upon the amplitude of said load signal falling outside of theupper and lower limits of an amplitude range encompassing said highamplitude discrimination value.

23. In a system for monitoring the operation of a well pumping unit ofthe type having a rod string and means for reciprocating said rod stringto operate a downhole pump, the improvement comprising:

transducer means connected to said well pumping unit for generating asignal representative of load changes in said unit as said rod string isreciprocated,

operator means responsive to said load signal for differentiating saidload signal to produce an operating function which is a derivative ofsaid load signal,

means for amplitude discriminating said operating function with respectto a specified discrimination value to produce a residual functioncomprised of a plurality of pulses characteristically proportional tothe amplitude differentials between the corresponding peaks of saidoperating function and said discrimination value, means responsive tothe output from said amplitude discriminating means for integrating saidresidual function, and means responsive to the output from saidintegrating means for generating a monitor function upon said outputreaching a specified constraint. 24. The system of claim 23 wherein saidpulses are proportional in duration to said amplitude differentials.

25. The system of claim 23 further comprising:

clipper means interposed between said transducer means and operatingmeans for clipping said load signal with respect to a peak amplitudereference value whereby said operator means differentiates said clippedload signal.

26. The system of claim 25 further comprising:

second discriminator means responsive to said load signal for amplitudediscriminating said load signal with respect to a high amplitudediscrimination value to produce a residual of said load signal, and

amplitude discrimination value.

150-1050 I UNITED STATES PATENT OFFICE v c 79'45 CERTIFICATE OFCORRECTION Patent 3,838,597 Dated October 1, 1974 Inventm-(S) RichardC.Montgomery and Jacque R. Stoltz It is certified that error appears inthe above-identified patentand that said Letters Patent are herebycorrected as shown below:

I- v I v '1 Column 7, line 45, delete "circuit".

Column 8, line 6, "uniit" should .be --unit--;

line 7, "donw" should be --down-; line 8, "pujping" should be--pumping-- Column 12, line 46 (claim 16, line 1), "The system of claim4" should be --The system of claim l4--.

Signed "and vsealed this 3rd day of December 1974.

(SEAL) I Attest:

MCCOY M. GIBSON JR. c. MARSHALL DANN Attesting Officer 7 Commissioner ofPatents

1. In a method of monitoring the operation of a well produced by theoperation of a pumping unit including a sucker rod string and means toreciprocate said rod string to produce fluid from a subterraneanlocation, the steps comprising: a. generating a signal representative ofa changing load in said unit as said rod string is reciprocated, b.operating on said signal to produce an operating function representativeof the rate of change of said signal, and c. generating a monitorfunction in response to said operating function reaching a specifiedcondition.
 2. The method of claim 1 further comprising the step of,prior to step (b), clipping said load signal with respect to a peakamplitude reference value, and carrying out the operation of step (b) onsaid clipped load signal.
 3. The method of claim 1 further comprisingthe step of amplitude discriminating said operating function to producea residual function thereof, accumulating said residual function, andgenerating said monitor function in response to said accumulatedresidual function reaching a specified constraint.
 4. The method ofclaim 1 wherein said load signal is differentiated to produce aderivative of said load signal as said operating function, amplitudediscriminating said operating function with respect to a discriminationvalue to produce a residual of said operating function comprising aplurality of pulses characteristically proportional to the amplitudedifferentials between the corresponding peaks of said operating functionand said discrimination value, integrating said residual function, andgenerating said monitor function in response to said integrated residualfunction reaching a specified constraint.
 5. The method of claim 4wherein said pulses are proportional in duration to said amplitudedifferentials.
 6. The method of claim 1 further comprising: comparingsaid load signal with an amplitude range having an upper amplitude limitand a lower amplitude limit, and generating a monitor function inresponse to the amplitude of said load signal falling outside of saidrange.
 7. The method of claim 1 further comprising: amplitudediscriminating said load signal with respect to a high amplitudediscrimination value, and generating a monitor function in response tosaid load signal failing to reach said value within a specifiedfrequency condition.
 8. The method of claim 7 further comprising thestep of, prior to step (b) of claim 1, clipping said load signal withrespect to a peak amplitude reference value which is less than said highamplitude discrimination value, and carrying out the operation of step(b) on said clipped load signal.
 9. The method of claim 7 furthercomprising: comparing said load signal with an amplitude range having anupper amplitude limit and a lower amplitude limit, said upper amplitudelimit being greater than said high amplitude discrimination value, andgenerating a monitor function in response to the amplitude of said loadsignal falling outside of said range.
 10. In a system for use inmonitoring the operation of a well pumping unit of the type having a rodstring and means for reciprocating said rod string to operate a downholepump, the combination comprising: transducer means adapted to beconnected to a well pumping unit of the type described for generating asignal representative of a changing load in said unit, operator meansresponsive to said load signal for producing an operating functionrepresentative of the rate of change of said load signal, and meansresponsive to said operating function for generating a monitor functionupon said operating function reaching a specified condition.
 11. Thesystem of claim 10 further comprising: discriminator means responsive tosaid load signal for amplitude discriminating said load signal withrespect to a high amplitude discrimination value to produce a residualof said load siGnal, and timing means responsive to the residual outputsignal from said discriminator means for generating a second monitorfunction upon said load signal failing to reach said high amplitudediscrimination value within a specified frequency condition.
 12. Thesystem of claim 11 further comprising: means responsive to saidfirst-named monitor function for disabling the operation of said timingmeans to generate said second-named monitor function.
 13. The system ofclaim 11 further comprising: comparator means responsive to said loadsignal for generating a readout function upon the amplitude of said loadsignal falling outside of the upper and lower limits of an amplituderange encompassing said high amplitude discrimination value.
 14. In asystem for use in monitoring the operation of a well pumping unit of thetype having a rod string and means for reciprocating said rod string tooperate a downhole pump, the combination comprising: transducer meansadapted to be connected to a well pumping unit of the type described forgenerating a signal representative of load changes in said unit,operator means responsive to said load signal for differentiating saidload signal to produce an operating function which is a derivative ofsaid load signal, means for amplitude discriminating said operatingfunction with respect to a specified discrimination value to produce aresidual function comprised of a plurality of pulses characteristicallyproportional to the amplitude differentials between the correspondingpeaks of said operating function and said discrimination value, meansresponsive to the output from said amplitude discriminating means forintegrating said residual function, and means responsive to the outputfrom said integrating means for generating a monitor function upon saidoutput reaching a specified constraint.
 15. The system of claim 14wherein said pulses are proportional in duration to said amplitudedifferentials.
 16. The system of claim 4 further comprising: clippermeans interposed between said transducer means and operating means forclipping said load signal with respect to a peak amplitude referencevalue whereby said operator means differentiates said clipped loadsignal.
 17. The system of claim 16 further comprising: seconddiscriminator means responsive to said load signal for amplitudediscriminating said load signal with respect to a high amplitudediscrimination value to produce a residual of said load signal, andtiming means responsive to the residual output signal from said secondamplitude discriminating means for generating a second monitor functionupon said load signal failing to reach said high amplitudediscrimination value within a specified frequency condition.
 18. Thesystem of claim 17 further comprising comparator means responsive tosaid load signal for generating a third monitor function upon theamplitude of said load signal falling outside of the upper and lowerlimits of an amplitude range encompassing said high amplitudediscrimination value.
 19. In a system for monitoring the operation of awell pumping unit of the type having a rod string and means forreciprocating said rod string to operate a downhole pump, theimprovement comprising: transducer means connected to said well pumpingunit for generating a signal representative of a changing load in saidunit as said rod string is reciprocated, operator means responsive tosaid load signal for producing an operating function representative ofthe rate of change of said load signal, and means responsive to saidoperating function for generating a monitor function upon said operatingfunction reaching a specified condition.
 20. The system of claim 19further comprising: discriminator means responsive to said load signalfor amplitude discriminating said load signal with respect to a highamplitude discrimination value to produce a residual of said loadsignal, and timing means responSive to the residual output signal fromsaid discriminator means for generating a second monitor function uponsaid load signal failing to reach said high amplitude discriminationvalue within a specified frequency condition.
 21. The system of claim 20further comprising: means responsive to said first-named monitorfunction for disabling the operation of said timing means to generatesaid second-named monitor function.
 22. The system of claim 20 furthercomprising: comparator means responsive to said load signal forgenerating a readout function upon the amplitude of said load signalfalling outside of the upper and lower limits of an amplitude rangeencompassing said high amplitude discrimination value.
 23. In a systemfor monitoring the operation of a well pumping unit of the type having arod string and means for reciprocating said rod string to operate adownhole pump, the improvement comprising: transducer means connected tosaid well pumping unit for generating a signal representative of loadchanges in said unit as said rod string is reciprocated, operator meansresponsive to said load signal for differentiating said load signal toproduce an operating function which is a derivative of said load signal,means for amplitude discriminating said operating function with respectto a specified discrimination value to produce a residual functioncomprised of a plurality of pulses characteristically proportional tothe amplitude differentials between the corresponding peaks of saidoperating function and said discrimination value, means responsive tothe output from said amplitude discriminating means for integrating saidresidual function, and means responsive to the output from saidintegrating means for generating a monitor function upon said outputreaching a specified constraint.
 24. The system of claim 23 wherein saidpulses are proportional in duration to said amplitude differentials. 25.The system of claim 23 further comprising: clipper means interposedbetween said transducer means and operating means for clipping said loadsignal with respect to a peak amplitude reference value whereby saidoperator means differentiates said clipped load signal.
 26. The systemof claim 25 further comprising: second discriminator means responsive tosaid load signal for amplitude discriminating said load signal withrespect to a high amplitude discrimination value to produce a residualof said load signal, and timing means responsive to the residual outputsignal from said second amplitude discriminating means for generating asecond monitor function upon said load signal failing to reach said highamplitude discrimination value within a specified frequency condition.27. The system of claim 26 further comprising comparator meansresponsive to said load signal for generating a third monitor functionupon the amplitude of said load signal falling outside of the upper andlower limits of an amplitude range encompassing said high amplitudediscrimination value.